(1) Field of Invention
The present invention relates to a system for tele-robotic control and, more particularly, to a system for tele-robotic control over time-delayed communication links.
(2) Description of Related Art
Tele-robotic operations at long distance (e.g., in space) face three main challenges: time delays in transmission and signal processing; limited situational awareness; and limited communication bandwidth. For example, for operations in the satellite disposal orbit, 300 kilometers (km) above the geostationary orbit (GEO), the speed-of-light communication imposes a lower limit on the delay (244 milliseconds (ms) round trip at 15 degrees inclination), which is further increased due to signal processing (typically >100 ms). With delays, teleoperations with a human and a robot in a closed loop becomes ineffective (see the List of Incorporated Cited Literature References, Literature Reference Nos. 1 and 2). A delay of 500 ms is considered disturbing, and a delay greater than 50 ms is noticeable. Moreover, delays can cause instabilities in robot control (see Literature Reference No. 3).
Several research efforts have dealt with compensating delays for teleoperating robots. One approach is a “bump and wait” strategy. With this strategy, the operator executes a command and waits until he/she observes its result. This strategy is usually tiring for the operator and leads to long overall execution times.
To improve operations, software has been suggested to predict the robot's movements on the operator's screen, referred to as a “predictive display” (see Literature Reference No. 4). This approach is limited by the requirement to accurately estimate the physics at the remote site. Particularly, the timing of contacts is almost impossible to predict more accurately than the delay.
Alternatively, Literature Reference No. 5 suggested a leader-follower model. Here, the operator plans the task in real time, while the robot tries to catch up with its execution; simultaneously, software on the operator's remote site checks for deviations against the plan and informs the operator. This approach requires a more high-level command-and-control structure and is unsuitable for more dexterous tasks with multiple contacts. Another alternative is to model the situation on the remote site and interact in closed loop with the model (see Literature Reference Nos. 6 and 7). Since the model does not need to be in closed loop with the remote site, delays and limits on the communication bandwidth are mitigated. However, this approach is limited by the accuracy of the model.
Each of the prior methods described above exhibit limitations that make them incomplete. Thus, a continuing need exists for a method that allows operator interactions with a model, but compensates for model inaccuracies. This method would enable the operator to practice robotic movements in simulation with a haptic device before they are executed on the robot.